Semiconductor devices are generally produced by a combination of two processes, i.e., a lithography technique and an etching technique. The lithography technique produces fine patterns on a photosensitive film such as a resist film coated on a surface of a material to be processed, such as a thin film of a semiconductor and a thin film of a magnetic material, which includes a photolithography technique where exposure is conducted with an ultraviolet ray, an electron beam lithography technique where exposure is conducted with an electron beam, and an ion beam lithography technique where exposure is conducted with an ion beam.
The etching technique is a technique of producing a device by transferring the resist pattern produced by the lithography to the material to be processed, such as a thin film of a semiconductor and a thin film of a magnetic material. Conventional etching technique includes a wet etching method, an argon ion milling method and a reactive ion etching method. Among these etching methods, the reactive ion etching method is popular because the pattern produced by the lithography can be precisely transferred.
In the reactive ion etching method, a material to be processed is placed in a plasma of a reactive gas with applying an electric field, and atoms on the surface of the material to be processed are chemically and physically removed by an ion beam incident normally onto the surface of the material to be processed, by which an anisotropic working is possible, where a part not covered with the mask is vertically cut along the edge of the mask. Accordingly, a fine and sharp feature can be transferred by the reactive ion etching method. In the reactive ion etching method, chemical active species such as an ion and a radical of the reactive gas generated in the plasma are adsorbed on the surface of the material to be processed, to chemically react with the material to be processed, and a surface reactive layer having lower bond energy. The surface of the material to be processed is exposed to the impact of cations accelerated by the electric field in the plasma, and thus the surface reactive layer having the lower bond energy is removed by the sputtering effect by ions or the evaporation effect of itself. That is, the reactive ion etching method is a process, which proceeds with a chemical action and a physical action simultaneously. As a result, the selectivity of etching only a specific material, and the anisotropy of vertically etching the surface of the material to be processed can be realized.